﻿#region Copyright

// ****************************************************************************
// <copyright file="PrimeNumberHelper.cs">
// Copyright © Vyacheslav Volkov 2012-2014
// </copyright>
// ****************************************************************************
// <author>Vyacheslav Volkov</author>
// <email>vvs0205@outlook.com</email>
// <project>MugenMvvmToolkit</project>
// <web>https://github.com/MugenMvvmToolkit/MugenMvvmToolkit</web>
// <license>
// See license.txt in this solution or http://opensource.org/licenses/MS-PL
// </license>
// ****************************************************************************

#endregion

using System;

namespace MugenMvvmToolkit.Infrastructure
{
    internal static class PrimeNumberHelper
    {
        #region Fields

        private const int MaxPrime = 2146435069;

        private static readonly int[] Primes;

        #endregion

        #region Constructors

        static PrimeNumberHelper()
        {
            Primes = new[]
            {
                3, 7, 11, 17, 23, 29, 37, 47, 59, 71, 89, 107, 131, 163, 197, 239, 293, 353, 431, 521, 631, 761, 919,
                1103, 1327, 1597, 1931, 2333, 2801, 3371, 4049, 4861, 5839, 7013, 8419, 10103, 12143, 14591,
                17519, 21023, 25229, 30293, 36353, 43627, 52361, 62851, 75431, 90523, 108631, 130363, 156437,
                187751, 225307, 270371, 324449, 389357, 467237, 560689, 672827, 807403, 968897, 1162687, 1395263,
                1674319, 2009191, 2411033, 2893249, 3471899, 4166287, 4999559, 5999471, 7199369
            };
        }

        #endregion

        #region Methods

        internal static int ExpandPrime(int oldSize)
        {
            int min = 2*oldSize;
            if (min > MaxPrime && MaxPrime > oldSize)
                return MaxPrime;
            return GetPrime(min);
        }

        internal static bool IsPrime(int candidate)
        {
            if ((candidate & 1) != 0)
            {
                var limit = (int) Math.Sqrt(candidate);
                for (int divisor = 3; divisor <= limit; divisor += 2)
                {
                    if ((candidate%divisor) == 0)
                        return false;
                }
                return true;
            }
            return candidate == 2;
        }

        internal static int GetPrime(int min)
        {
            for (int i = 0; i < Primes.Length; i++)
            {
                int prime = Primes[i];
                if (prime >= min)
                    return prime;
            }
            for (int i = (min | 1); i < Int32.MaxValue; i += 2)
            {
                if (IsPrime(i))
                    return i;
            }
            return min;
        }

        #endregion
    }
}